1. Field of the Invention
The present invention relates in general to a device for controlling a variable geometry turbocharger by controlling the supercharging pressure through varying the exhaust gas volume in an automobile turbine according to the RPM and load on the engine, and more specifically, to a variable geometry tubocharger control device to provide an increase in torque and improvement in acceleration over the full range of engine operation, especially when accelerating.
2. Description of the Prior Art
In a conventional supercharging pressure control device for a variable geometry turbine, a movable member is provided which varies the channel surface area of an internal turbine housing which incorporates a scroll. The capacity of the turbine is varied by moving this member, thus providing control of the supercharging pressure over the entire operating range of the engine and improvement of the intake air combustion efficiency under acceleration.
However, in this type of conventional control device, with only a variable geometry mechanism which moves the movable member to provide a structure for controlling the supercharging pressure over the entire operating region, when the movable member is moved, the range in which the channel surface area of the scroll can be varied is limited. Control of the supercharging cannot be provided in a region which deviates from the range of movement of this variable geometry mechanism, that is, outside of the range in which the movable member moves, especially in the low and high velocity ranges. As a result, the efficiency of the turbine deteriorates, and this can create the drawback of causing the supercharging pressure to drop. In addition, because a stable supercharging pressure is not possible when accelerating from the low speed range to the high speed range, the difficulty of stimulation of an increase in torque over the entire operating range of the engine, and providing a satisfactory improvement in acceleration, become problems. Accordingly, there is an urgent requirement for a method of providing supercharging pressure control beyond the range of movement of the movable member, and increasing the supercharging pressure.